Conventionally, used injection needles are not reused but are thrown away to prevent viral infection or the like. In the case where the needles cannot be thrown away immediately after use, in order to prevent the needles from accidentally sticking someone, the caps (see, for example, JP 8(1996)-10328 A and JP 8(1996)-206202 A) that had been put thereon when the injection needles were delivered are put on the used injection needles again.
However, conventional caps that are used for safeguarding injection needles are attached to the injection needles merely through, for instance, insertion or press fit. This poses a problem that it is difficult to judge from their appearance whether the conventional injection needles with caps being put thereon have been used or have not been used. Furthermore, in the case of conventional injection needles, there is a probability that used injection needles may be reused by mistake due to the difficulty in distinguishing therebetween.